Spatial mapping of rice leaf area index using UAV-borne RGB and multispectral data: a comparison of Beer-Lambert law and machine learning algorithms
摘要
Accurate monitoring of Leaf area index (LAI) is essential in precision agriculture. This study aimed to enhance the accuracy of rice LAI estimation by integrating Grey level co-occurrence matrix (GLCM) textural features, spectral bands (SB), color indices (CIs), vegetation indices (VIs), and plant height; and by employing machine learning (ML) models and Beer-Lambert Law. The UAV-based RGB and multispectral (MS) sensors were used to collect the images from two seasons (2023 and 2024) of rice grown in Roorkee, Uttarakhand, India. Five ML models were employed, Extreme Gradient Boosting (XGBoost), Support Vector Machine (SVM), K-Nearest Neighbors (KNN), Random Forest (RF), and Artificial Neural Network (ANN) with three feature selection methods: Least Absolute Shrinkage and Selection Operator (LAS), Maximal Information Coefficient (MIC), and Recursive Feature Elimination (RFE). A total of 75 input features were utilized. Among all the model combinations, XGBoost-RFE (R2 = 0.86, NRMSE = 15%) had the highest prediction accuracy. The three combinations of the RF model (RF-MIC, RF-RFE, and RF-LAS) performed similarly (R2 = 0.85, NRMSE = 16%), and their performance was comparable to that of XGBoost-RFE (R2 = 0.86) and the Beer-Lambert law (R2 = 0.83). The GLCM Dissimilarity Green textural feature highly influenced the rice LAI. The color indices, including EG, ER, WI, GLA, EXGR, and EB; spectral bands RedEdge, NIR, Green, Red, and Blue; and VIs comprising RVI, NDI, and ENDVI affected the rice LAI. Overall, UAV-based RGB and MS imagery coupled with ML models successfully predicted rice LAI, offering a reliable solution for precision crop monitoring.